Telephone signal receiver



Dec. 14, 1943. w. 51x ETAL 2,336,768

TELEPHONE SIGNALRECEIVER Filed on. '2. 1939 2 Sheets-Sheet 1 Patented Dec. 14, 1943 TELEPHONE SIGNAL RECEIVER Willem Six and Frank de Fremery, Eindhoven, Netherlands, assignors, by mesne assignments, to Hartford National Bank and Trust Company, 'Hartford, Conn., as trustee Application October 2, 1939, Serial No. 297,576 In Germany September 12, 1938 4 Claims.

This invention relates to signal receivers such as are used in telephone practice for the reception of ringing or calling signals.

It is known to transmit calling signals over a telephone line by means of a carrier frequency of, say, 500 cycles per second which is interrupted periodically, for example, at a frequency of 20 cycles per second. In such a case the calling signals consist of a series of successive impulses having a duration of A sec. and having a carrier frequency of 500 cycles per second. On the receiving end, i. e. at the end of the telephone line, a. signal receiver is provided whose circuit arrangement is such that it responds only to the signal currents and not to those speech-modulated currents which are received during the conversation and whose frequencies are equal or close to those of the signal. For this purpose it has been proposed to employ a two-fold frequency selection by using an oscillatory circuit which is tuned to the carrier frequency of 500 cycles per second so as to filter out the speech currents. The selected output is rectified so that after rectification the interruption frequency of 20 cycles per second is obtained and is passed through a second oscillatory circuit. This second circuit is tuned to the interruption frequency and its output is used to control a relay which'controls the signal circuit.

The main object of our invention is toprovide a signal receiver of relatively simple construction which prevents false response of the signal circuit due to speech currents.

The signal receiver according to the invention, employs a time lag principle in such a manner that the signal circuit is not actuated until a definite number of successive impulses of the carrier frequency have been received within a definite time. For this purpose the interruption frequency obtained after rectification of the received signal is supplied to a network of condensers and rectifiers connected in a voltage-multiplier arrangement whose output circuit controls the signal circuit.

In order that the invention may be clearly understood and readily carried intoeffect, we shall describe the same in more detail with reference to the accompanying drawings in which:

Figure 1 is a schematic diagram of a signal receiver according to the invention, and

Figs. 2 to 12 are voltage-time curves showing the voltages at various points of the receiver of Figure l.

In Figure l the signal currents received over a telephone line l-Z are supplied through resistances 3 and 4 to'the primary winding 6 of a transformer 5 whose secondary winding 1 is tuned by a condenser 8 to the carrier frequency of the signaling currents. Winding 1 has one end connected through a grid condenser 9 to the grid of a triode tube ll whose cathode is connected to the other end of winding 1 and to ground. A

grid leak resistance In is connected across the grid and cathode of tube II. The resistances 3 and 4 serve to increase the input impedance of the signal receiving circuit so that the shuntin effect on the telephone line is negligible.

The tube ll acts as a grid detector 50 that a voltage having the frequency of the interruptions of the signal currents as well as the frequency of the carrier current, is produced across a resistance l3 connected in series with a battery I5 in the plate circuit of triode l I. A condenser I2 is connected between the plate and cathode of tube II. a

The voltage component having the interruption frequency is supplied through a resistance I4 to a condenser I6. The resistances l3 and I4 and the condensers l2 and [6 are given such values that the voltage E16, 1. e. the voltage across condenser l6, will be substantially equal to the voltage of the interruption-frequency superimposed upon a D. C. voltage E15 (later to be referred to) which is the D. C, voltage existing between the anode and the cathode of the tube I l.

According to the invention, this voltage Em is applied to a voltage-multiplier comprising a network of condensers l1, I9, 22 and 24, and rectifiers 20, 2|, 23 and 25. More particularly, the rectifiers are connected in series and a condenser shunts each pair of successive rectifiers, The rectifiers pass current in the direction indicated by the arrows. One output terminal 30 of the network is connected through a grid bias battery l8 to ground and the other terminal 34 is connected to the grid of an amplifying tube 26. A

relay 2'! having a normally-open contact 40 adapted to control a signal circuit 28 has its coil connected in the plate circuit of tube 26.

The operation of the device of Figure 1 and the voltage across the different points thereof will be described in connection with the curves of Figures 2 to 12. The curve of Figure 2 shows the signal impulses received over lines |2 by interrupting a carrier wave of 500 cycles per second at a frequency of 20 cycles per second sothat the signal impulses have a duration of /40 of a second. Figure 3 shows the voltage Em across condenser l6. 1. e. between points 29 and 3|. Figure 4 shows the voltage E11 across condenser H i. e.'the voltage between points 3| and 33. Figure 5 shows the volta e Ere-a: across the series connection of the rectifier 20 and the battery l8, 1. e. between point 33 and the grounded point 23. Figure 6 shows the voltage Eat-a3 across rectifier 20 i. e. between points 33 and 30. Figure 7 shows the voltage E19 across condenser I9 1. e. between points 30 and 32. Figure 8 shows the voltage Eae-aa across rectifier 2| i. e. the voltage between points 32 and 33. Figure 9 shows the voltage E22 across condenser 22 i. e. between points 33 and 35. Figure 10 shows the voltage Ear-35 across rectifier 23 i. e. between points 32 and 35. Figure 11 shows the voltage E2 across condenser 24 i. e. between points 32 and 34. Figure 12 shows the grid voltage of tube 26 i. e. the voltage between points 29 and 34.

The operation of the network of condensers and rectlflers in a voltage-multiplier are known in the art and are described, for example, in the U. S. Patent #1,974,328, dated September 18, 1934, to Albert Bouwers.

From the curves of Figures 3 to 12 it is seen that each of the condensers l9 and 24 is charged to a voltage E which is equal to the amplitude of the impulses of the voltage E16 on the condenser 18 (see Fig. 3) and is in a direction such that the point 32 is E volts more negative than point 30 and that point 34 in turn is E volts more negative than point 32. Thus, a voltage of 2E volts exists across points 34 and 30. Consequently, when signal impulses are received over the lines I and 2 the negative bias of the grid of tube 26, which bias has value Eu; 1. e. the voltage of battery I8, is decreased by the amount 2E with the result that the anode current of tube 26 is decreased causing the relay 2] to become demagnetized and close contact 40 and thereby establish signal circuit 28.

The above-described doubling of the voltage may be extended by adding further rectifiers and condensers to the voltage-multiplier. As is shown in Fig. 12, the voltage on the grid of tube 26 varies in three steps, namely one step equal to E1a, a second step equal to (E1s-E) and a third step equal to (Em-2E). The first step takes place at the end of the first impulse of 500 cycles (see Fig. 2), the second step takes place at the end of the second impulse, i. e. & second later, and so on. When the grid voltage is E1a, i. e. during the first step, the anode current of tube 26 has so high a value that the armature 40 is open (as shown). The armature is not released until the grid voltage reaches a value (E1anE), i. e. at the end of the nth impulse. It is clear that at least a multiplication of the voltage E by n must take place to deniagnetize .the relay at the end of a-series of impulses of 500/20 cycles.

The condensers I1, I21, 22 and 24 are given such capacities and the rectifiers 20, 2|, 23 and 25 are given such resistances in the blocking direction that the condensers substantially retain their charges when impulses of the interruption-frequency of 20 cycles are received. If, during the transmission of speech currents impulses of 500 cycles are received temporarily, condenser I9 will be charged (see Fig. 7) but it loses its charge due to the discharge through the blocking resistance of the rectifiers 20 and 2| before the next impulse of 500 cycles occurs in the conversation. Separate impulses of 500 cycles in the speech current which occur with larger time intervals, cannot alter the grid voltage of tube 26 by more than a voltage E; so that false response of the signal circuit 28 to speech current impulses is avoided. It will be clear that the safety against false response to speech current impulses is increased by making the receiver only responsive to signalling currents consisting of a greater number of impulses than above illustrated, i. e. by embodying in the receiver a larger number of condenserrectifier combinations in the voltage-multiplier.

If the speech current impulses of 500 cycles are received in more rapid succession than 20 per second, the frequencies received are located outside the band of frequencies of from 480 to 520 cycles. These frequencies are not passed by the resonance circuit formed by winding 1 and condenser 8 at the entrance of the signal receiver and consequently cannot give cause to false response of the signal circuit 28. v

The curves of Figures 4 to 12 have been drawn for the ideal case in which the blocking resistance of the rectifiers has an infinitely high value. In practice the condensers slowly lose their'charges so that after termination of the last signal impulse the relay again attracts the armature 43 with a certain time-lag.

It is evident that the circuit-arrangement may be such that, instead of the signal circuit being established by a decrease in the grid voltage of tube 25 (a more negative grid voltage), it is established by an increase of the grid voltage (a more positive grid voltage). For this purpose the arrangement is such that, in the absence of calling signals, the current passing through the coil of relay 2'! is small and the armature is opened whereas upon the reception of calling signals the grid voltage of the tube 26 becomes more positive and the anode current thereof thereby magnetizing the relay 2! to attract armature 40 and establish the signal circuit 28.

Although we have described our invention with reference to a specific arrangement and a certain application, we do not desire to be limited thereto because obvious modifications will present themselves to one skilled in the art.

What we claim is:

1. A signal receiver for controlling a signal circuit from consecutive signal impulses transmitted by a periodically-interrupted carrier oscillation, comprising means for rectifying said carrier oscillation and deriving therefrom a number of voltage impulses corresponding to said signal impulses, means to multiply the voltage of said voltage impulses in an accumulative and step-like manner to produce an amplified voltage proportional to the number of said voltage impulses, and means actuated by the amplified voltage to control the signal circuit when the amplified voltage attains a value corresponding to a predetermined number of signal impulses.

2. A signal receiver for controlling a signal circuit from consecutive signal impulses transmitted by a periodically-interrupted carrier oscillation, comprising means for rectifying said carrier oscillation and deriving therefrom a number of voltage impulses corresponding to said signal impulses, means to multiply the voltage of said voltage impulses in an accumulative and steplike manner to produce an amplified voltage proportional to the number of said voltage impulses, said latter means comprising a plurality of condensers and rectifiers, the rectifiers being connected in series and a condenser shunting each pair of successive rectifiers, and means actuated by the amplified voltage to control the signal circuit when the amplified voltage attains a value corresponding to a predetermined number of si nal impulses.

3. A signal receiver for controlling a signal circuit from consecutive signal impulses transmitted by a periodically-interrupted carrier oscillation, comprising a resonance circuit tuned to the frequency of the oscillation, means for rectifying the oscillation passed by said resonance circuit and deriving therefrom a number of voltage impulses corresponding to said signal impulses, means to multiply the voltage of said voltage im pulses in an accumulative and step-like manner to produce an amplified voltage proportional to the number of said voltage impulses, said voltage multiplier comprising a plurality of series connected rectiflers and a plurality of condensers each shunting a pair of successive rectifiers,'and means actuated by the amplified voltage to control the signal circuit when the amplified voltage attains a value corresponding to a predetermined number of signal impulses.

4. A signal receiver for controlling a signal circuit from consecutive signal impulses transmitted by a periodically-interrupted carrier oscillation, comprising a resonance circuit tuned to the frequency of the oscillation, means for rectifying the oscillation passed by said resonance circuit and deriving therefrom a number of voltage impulses corresponding to said signal impulses, a

resistor and condenser connected in series across the output of said rectifying means, a voltage multiplier connected across said condenser and comprising a. plurality of series-connected rectifiers and a plurality of condensers each shunting a pair of successive rectifiers, a grid controlled tube, a grid circuit for said tube connected to the output of said voltage multiplier, a plate circuit for said tube, means in said plate circuit to control the signal circuit, said signal circuit being actuated only when the voltage derived from the voltage multiplier attains a value corresponding to a predetermined number of signal impulses. 1 1 WILLEM SIX.

FRANK 1m FREMERY. 

